It is generally believed that defocus blur provides the primary stimulus for the accommodative system. Our investigations now support the view that accommodation responds to a variety of both dioptric and nondioptric stimuli. The proposed experiments will examine these two categories of stimuli by concentrating on the following: 1) the chromatic cues that result from the chromatic aberration of the eye; and 2) changes in target size and apparent distance. The research involves the development of a versatile stimulus system that will be used along with an infrared recording optometer to determine the mode of action of the stimuli, their relative importance, and how they interact with other stimuli such as defocus blur. Specifically the aims of the experiments are to (1) determine the frequency response of the accommodative system to defocus blur while the effects of the chromatic aberration of the eye are manipulated by achromatizing lenses and monochromatic light; (2) determine the frequency response of the accommodative system to changes in the wavelength of light--the color of the target will change in a sinusoidal manner; (3) determine the frequency response of the accommodative system to defocus blur under isoluminant stimulus conditions; (4) examine the relative importance of target size and defocus blur as stimuli for accommodation by stepping the stimuli (size and blur) in opposite directions; (5) examine the relative importance of changing size and changes in apparent distance on the accommodative response; (6) examine the relative importance of size change and velocity of size change as stimuli by using ramp and step-ramp changes in target size. The investigation will confirm that accommodation responds to a variety of dioptric and non-dioptric stimuli and the findings may therefore have implications for the treatment of a range of vision anomalies such as accommodative infacility, myopia and amblyopia.